Currently, there is a need to preserve natural resources and reduce dependence on landfills and similar waste storage facilities. To meet this need, several processes and machines are used to identify and sort waste materials, such as glass. Glass containers and other glass objects are recycled by first crushing or breaking the glass into glass cullet, which are small pieces of glass of varying characteristics that are distinguished by color. Prior to recycling, glass cullet of varying colors and types are placed on a conveyer belt and need to be separated and sorted.
The cullet are then identified and sorted based on the respective color or type of the cullet. For example, a typical collection of glass cullet may include pieces of borosilicate, soda-lime, and flint glass each of which may include clear, red, green and blue color components and combinations as well as contaminants. Prior art glass sorting machines that sort by color function by passing the pieces of cullet (hereinafter referred to as “cullet”) in a “waterfall” between colored LED light sources and light sensors arranged to define a sensing area. The cullet have different color characteristics which attenuate the light emitted from the light source in different amounts. For instance, a red colored cullet passed between a series of red and green light sources is identified as a red cullet based on attenuated light characteristics.
U.S. Pat. No. 5,314,071 to Christian et al. teaches a method of purification and color sorting of waste glass as well as a glass beneficiation process and apparatus. Christian et al. teach a method of sorting glass based on the transmission properties of the glass using red and green lamps. In addition, Christian et al. detail a method of using an actuator to deflect the trajectory of the glass. The deflection causes the glass to descend into one of two paths, which is the undeflected trajectory and the deflected trajectory. The specifics of the prior sorting system is taught and described in U.S. Pat. No. 5,314,071 to Christian et. al, which is hereby incorporated by reference.
As full scale glass beneficiation has become more prevalent, the disadvantages of the system and method taught in Christian et al. have been realized. First, the red and green lamps taught in Christian et al. limit the spectral response of the system. Glass entering the beneficiation plants contains shades of green, brown or blue that cannot be differentiated with a red and green lamp. A second disadvantage by the system taught in Christian et al., is that Christian et al. describe a means to deflect the trajectory of the descending glass with a single actuator, which is termed a binary sort. Therefore, the single actuator in Christian et al. performs several sorting stages to arrive at a pure material. Additional sorting stages add cost, energy and time to the equipment and sorting process. A third disadvantage of the system taught in Christian is its inability to distinguish between different glass types.
Other prior art machines sort by type use x-ray fluorescence to produce a x-ray fluorescence spectrum from cullet of unknown composition. By comparing the x-ray fluorescence spectrum with x-ray fluorescence spectra of known materials, the sorting machines classify the unknown cullet as one of several possible materials.
U.S. Pat. No. 6,888,917 to Sommer, Jr. et al. describes a system and process for classifying a piece of material using a high intensity x-ray source. Material moves along a conveyer belt and through a detection chamber where it is exposed to x-rays. The x-rays cause the material to fluoresce and produce an x-ray fluorescence spectrum, which is detected and used to classify the material. Then material moves along a conveyer belt through a series of decision points. At a decision point corresponding to its classification, the material is selectively removed from the conveyer belt by an actuator.
As full scale glass beneficiation has become more prevalent, the disadvantages of the system and method taught in Sommer, Jr. et al. have been realized. The system taught by Sommer uses an x-ray source, which requires high power and produces dangerous radiation, necessitating safety precautions. A second disadvantage of the system taught in Sommer is its use of a single actuator to accomplish a binary sort at each decision point; multiple decision points are sequenced to provide several sorting operations. The sequential nature of the sort requires more time and a larger conveyer belt surface than a system which accomplishes a more complex sort at each decision point. Additional decision points add cost, energy and time to the equipment and sorting process. A third disadvantage of the system taught in Sommer is its inability to distinguish between different glass colors.
In addition, the current actuators are air driven jets which shoot air at the cullet to deflect the cullet into their desired trajectories. However, small cullet having a dimension of less than 0.25 inches are unable to be properly sorted with air jets actuators due to the delay associated with air jet actuators. The valve within the air jet actuator is designed to require 3 to 5 milliseconds of pressure buildup before the actuator is able to discharge the adequate amount of forced air at the cullet. In addition, the compressibility characteristics of air prevents the actuator from quickly discharging and directing the compressed air to the falling cullet. Thus, the design and characteristics of air driven actuators cause the devices and the system in general to be relatively slow and inefficient.